Separate numbers, strings from one line using bash

Question

How to separate strings and numbers from one line using a bash command.

Example: I have a string containing

string123anotherstr456thenanotherstr789

The output should be:

string
123
anotherstr
456
thenanotherstr
789

Answer 1

GNU grep or compatible solution:

s="string123anotherstr456thenanotherstr789"
grep -Eo '[[:alpha:]]+|[0-9]+' <<<"$s"

• [[:alpha:]]+|[0-9]+ - regex alternation group, matches either alphabetic character(s) or number(s); both will be considered as separate entries on output

The output:

string
123
anotherstr
456
thenanotherstr
789

Answer 2

awk

Input contains only letters and numerals

Add a newline character after every [[:alpha:]]+ (sequence of letters) and after every [[:digit:]]+ (sequence of numerals):

awk '{ gsub(/([[:alpha:]]+|[[:digit:]]+)/,"&\n",$0) ; printf $0 }' filename

(The & is awk shorthand for the matched sequence.)

---

Input contains other characters (eg, punctuation)

As before, but now also dealing with substrings of [^[:alnum:]]+ (non-letter, non-numeral) characters:

awk '{ gsub(/([[:alpha:]]+|[[:digit:]]+|[^[:alnum:]]+)/,"&\n",$0) ; printf $0 }' filename

---

Negative numbers and decimal fractions

Treat - (hyphen) and . (period) as numbers:

awk '{ gsub(/([[:alpha:]]+|[[:digit:].-]+|[^[:alnum:].-]+)/,"&\n",$0) ; printf $0 }' filename

Those characters must appear in both the [[:digit:].-]+ and [^[:alnum:].-]+ expressions. Also, to be interpreted as a literal hyphen, the - must be last character before the final right square bracket of each expression; otherwise, it indicates a range of characters.

Example:

[test]$ cat file.txt 
string123another!!str456.001thenanotherstr-789

[test]$ awk '{ gsub(/([[:alpha:]]+|[[:digit:].-]+|[^[:alnum:].-]+)/,"&\n",$0) ; printf $0 }' file.txt 
string
123
another
!!
str
456.001
thenanotherstr
-789

---

An exercise for the reader

If the input file requires it, you could modify the awk command to:

• Ensure that - only counts as part of a number if it occurs at the start of a numeral sequence.
• Allow numbers that are expressed in scientific notation.

Answer 3

POSIXly:

string=string123anotherstr456thenanotherstr789
sed '
  s/[^[:alnum:]]//g; # remove anything other than letters and numbers
  s/[[:alpha:]]\{1,\}/&\
/g; # insert a newline after each sequence of letters
  s/[0-9]\{1,\}/&\
/g; # same for digits
  s/\n$//; # remove a trailing newline if any' << EOF
$string
EOF

Answer 4

GNU sed (or compatible) solution:

s="string123anotherstr456thenanotherstr789"
sed 's/[a-zA-Z]*\|[0-9]*/&\n/g; s/\n$//' <<<"$s"

The output:

string
123
anotherstr
456
thenanotherstr
789

Answer 5

python3

python3 -c '
from itertools import groupby
s = ("".join(g) for k, g in 
    groupby("string123anotherstr456thenanotherstr789", lambda x: x.isalpha()))
print(*s, sep="\n")
'

string
123
anotherstr
456
thenanotherstr
789

Answer 6

Used below one liner to achieve the same. As tested its worked fine

sed "s/[0-9]\{3\}/\n&/g" filename | sed "s/[0-9]\{3\}/&\n/g"| sed '/^$/d'

output

string
123
anotherstr
456
thenanotherstr
789

Answer 7

I didn't see a Perl solution yet, so here:

$ cat s
string123anotherstr456thenanotherstr789
$ perl -lne 'print $& while /[[:alpha:]]+|[[:digit:]]+/g' < s
string
123
anotherstr
...

Of course, for wider definitions of "numbers", we might want to use [-+]?[0-9]+ (leading sign), [-+]?[0-9]+(.[0-9]+)? (plus optional fractional part), or even [-+]?[0-9]+(\.[0-9]+)?([eE][-+]?[0-9]+)? (plus optional exponent). The latter two ones require at least one digit before and after the decimal point, if it is present.

Answer 8

Pure Bash

This is relatively inefficient because it makes several (shorter) copies of the original string:

declare s=string123anotherstr456thenanotherstr789
while [[ "$s" =~ ^([a-z]+)([0-9]+) ]]; do
  echo ${BASH_REMATCH[1]}
  echo ${BASH_REMATCH[2]}
  s="${s:${#BASH_REMATCH[0]}}"
done

How many letters-digits pairs per line are you dealing with?

Answer 9

gawk '{ $1 = $1; print }' FPAT='[a-z]+|[0-9]+' OFS='\n' input.txt

Testing

gawk '{ $1 = $1; print }' FPAT='[a-z]+|[0-9]+' OFS='\n' <<< 'string123anotherstr456thenanotherstr789'

Output

string
123
anotherstr
456
thenanotherstr
789